The present invention concerns a means for improving the stability of a tractor or other working machine in which a swivelling joint with horizontal axis has been connected to the body structure of the tractor or in conjunction with the wheel axles, this joint enabling the tractor's wheel axis to twist relative to each other when driving over rough terrain, and said tractor being provided with a work implement projecting beyond its frame, such as a loader and/or an excavator, which when loaded produces a moment tending to overturn the tractor when the tractor wheels are in a position turned to one side to for the purpose of steering.
For moving about in uneven terrain, the tractor and the work implement have as a rule been provided with some kind of swivelling joint which allows the tractor's wheel axles to twist with reference to each other. The structure cannot be made rigid since every tractor wheel must be able separately to conform to the terrain configuration, for instance to its dips and eminences. The swivelling axle may be disposed in the body of the tractor, or the axle of the tractor wheels may be designed to be a rocking axle.
Since to the body of the tractor large-sized work implements are often attached, such as loaders or excavators, the centre of gravity of the whole tractor tends to be quite high above the ground. Hereby, in some situations the stability of the tractor is impaired to the extent that the tractor may turn over. A situation like this is for instance incurred when the loader of the tractor is heavily loaded and simultaneously an abrupt turn to one side is executed with the tractor. Even an unloaded tractor may topple in an abrupt turn if the terrain is rough.
The stability problem is very serious in a body-steered tractor or working machine having a steering joint with vertical axis for moving the different parts of the tractor body with reference to each other. When a swivelling motion is induced about this joint, the axles attached to the parts of the body turn with them and in this way the tractor can be steered in the lateral direction. However, for moving over uneven terrain, a swivelling axle with horizontal axis has also been provided in the tractor, enabling the tractor's axles to twist with reference to each other, conforming to the configuration of the terrain. However, the swivelling axle renders the tractor exceedingly unstable in lateral direction. Large-sized work implements such as loaders may, when turned to one side, quite easily overturn a tractor of this kind.
In prior attempts to solve the above-mentioned tractor stability problem, for instance, the swivelling joint is not kept locked during normal driving in the terrain, and only when lifting a heavy load the swivelling axle is braced to be unturntable. However, such use of the tractor is inconvenient, and the driver is required to exercise great attentiveness so that he might always remember to carry out the required bracing measures. This procedure is still no guarantee that the tractor will never topple, because even an unloaded tractor may overturn in uneven terrain.